@davestewart: "Further to my last post about re-engining my boat I set to thinking
There are numerous diesel sets coming onto the market at the moment rated 
between 6 and 10 HP (some more) and they seem relatively inexpensive but 
also a bit light/small/flimsy ... you know what i mean. compare one of those 
at 50kg to a Volvo MD1 ....... at 4 tons :-)
could one of these be used to run a boat, by boat I mean a sailing boat 
where the engine usually only works to get in and out of a mooring an the 
occasional becalming. I sail in the Irish sea and if there is no wind I have 
to motor for about 2 hours to get out or back to my mooring the tidal steam 
can be four knots against me...
what are the cons?
another alternative would be a diesel genny running an ac motor via a 
controller or use the genny via a mega rectifier to run a dc motor with 
battery backup
what about one of the aforementioned diesel engines running a hydraulic pump 
and using that to run the prop (thanks dave)
Any thoughts "
    @davestewart: "for example
<url>
!9HP....probably will go for a lot less than �500
or
<url>
5KW diesel genny �700
and many more going at a lot less
any ideas....
rgds
Dave "
    @tony: "<quote>
In days of yore, when I was young, yachts had auxiliaries.  Modest HP purely
for getting on/off moorings and into harbours.  J's original engine (for
32ft, 7 tons) was a 9HP Saab (built to last forever, which was a good thing
as it would take forever to get anywhere).  Now Nic 32 owners are
re-engining with 25HP.
Whatever you have it is going to be no fun motoring against 4kns.
I shouldn't think these small engines are anywhere near marine standard of
construction.  Willing to be proved wrong though."
    @look: "<quote>
there is an old saying about buying a diesel by weight, like most of these
old sayings it is not without merit.
really depends on how much you fancy walking home when the engine fails.
a serious comment that applies to all auxiliary / single screw craft.
either that or use your sails and set your schedules by the tide.
diesel electric and diesel hydraulic are both known technologies in small
boats, trust me they are both far far more expensive than a simple
mechanical gearbox, but they win because some designers will like the
freedom for placing the engine anywhere in the hull they like.
fix your mechanical box, or replace it with another mechanical or hydraulic
box, all you care about REALLY is power handling and direction of rotation,
you then go buy a new prop to match, _if_ you end up with different ratios.
HTH etc
Lithium ion internal and external batteries.
Internal from �30 External from �75 (trade)
All batteries factory new and guaranteed.
<url>
e-mail <email_address> (<url>"
    @davestewart: "Hmmm you've just echoed my thoughts....still it was worth asking the 
question
thanks guys
"Guy Fawkes" <email_address> wrote in message 
news:hrH%d.21976$<email_address>
<quote>"
    @jassira53: "<quote>
A marine 6.3kva gen set would cost thousands of pounds.... how different are 
they...... is it feasble to install one of these, after all, if you through 
it away every fews years you still be quids in....."
    @look: "<quote>
R0 for return hoses and case drain and R1 for supply, the pressures as you
say are nothing special, nor are the flow rates of anything else, there is
nothing special about any of it, it just doesn't scale well engineering
wise or finance wise to 20 bhp and 40 ft/lb of torque....
JCB, caterpillar track driving motors etc, none of em are short of motive
power and none of em give a damn about efficiency.
same argument holds true for diesel electric on small boats, you have to no
care about efficiency and cost, or rather you have to care more about
something else.
Lithium ion internal and external batteries.
Internal from �30 External from �75 (trade)
All batteries factory new and guaranteed.
<url>
e-mail <email_address> (<url>"
    @look: "<quote>
the motor type you describe as "new" is older than my dad, who has been dead
15 years....
yes, the swash plate motors you describe are more efficient when driving a
load like a prop, because they are much lower torque than old style motors,
but, they are also much more leaky towards the case drain, they also are
usually with vane pumps, which also leak a lot to the case drain and do
generate a lot of heat.
indeed, and compare it to any offering from say caterpillar, and you will
see it is the "mini moto" to motorcycle analogy, the former is not a pukka
scaled down version of the latter, but a toy that was never meant to work
all day every day.
you need a gear splitter then to meter the flow equally to both prop motors,
and that costs as much as a pump.
which is going to work in a different way torque/rpm/load than a prop so
needs a reducer or a different pump to drive it properly
which is either going to be using another gear splitter or another pump or
it is going to be another bodge off the same supply circuit as the main
prop, which means speed variation problems when you run one and then cut
the other in because power will go the easy route, whichever that is, so
you'll also be needing the throttle riding to effect any sort of control.
is easy to do cheaply and very badly, yes.
no, a conventional gearbox does one job and one job only, but it does it
well.
absolute crap, overall mechanical efficiency of a mechanical gearbox blows
away hydraulic coupled pump / motor assemblies every time, depending on
load conditions by anything from a significant margin to a vast margin
convention mechanical gearboxes absorb about 3% of the power they transmit,
shaft bearings about 1.5%, that's pretty much across the board.
hydraulics can't even approach that on a good day with a tail wind under
idealised and totally unrealistic conditions, and I'm an old time
hydraulics fan and even I have to admit that.
and apart from efficiency we aren't going anywhere near installation costs,
maintenance costs, etc etc etc
Lithium ion internal and external batteries.
Internal from �30 External from �75 (trade)
All batteries factory new and guaranteed.
<url>
e-mail <email_address> (<url>"
    @marine: "news:<email_address>
<quote>
and
As
the
We
I speak as I find. We had endless problems with filters breaking up and the
result particles damaging the pumps with no warning. I rather suspect it wa
sto do with pressure pulses caused by going from hard ahead to hard astern.
I think these are transitory, very high, and too fast for the PRV to dump.
We also had cavitation damage in the early pumps and motors we were advised
to use. The particles from this - depite great big magnets in the tanks -
caused motior siezure again with no warning.
If my life might depend upon something, I want it to fail with warning and
gradually or in a repairable way. I know drive plates can fail without
warning, but that is because they are not checked frequently enough.
I know someone who intended to take a hydraulically powerd Caribbean cruiser
across the Channel - the ones with the large open front well deck. When I
asked him how he was going to navigate he said "go to Southend, turn right,
and when I see a ferry, follow it". All I know is that he left Maidenhead.
One can do all sorts of things in all sorts of conditions, but it is down to
the individual to make an INFORMED choice, hence my warnings.
Tony Brooks"
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